From Wikipedia:
The Panama Canal Zone (Spanish: Zona del Canal de Panamá) was an unorganized territory of the United States from 1903 to 1979, centered on the Panama Canal in the Republic of Panama.I don't know what SCOTUS ruled. but administrations and the military acted as if they were not on US territory. During WW-II all mail between US and Europe went through Bermuda where "censors" read it in violation of the 4th Amendment of the Constitution.